The spider that loses its penis during sex to make it more fierce in battle against love rivals

Losing its genitals, being eaten alive, or fighting off enemies: It's a tough life for nephilengys malabarensis

The phrase 'eunuch' has derogatory connotations for us humans - but it is a different matter for spiders.

The male nephilengys malabarensis spider loses its spider penis when it has sex with a female, which is in itself a clever (if potentially painful) evolutionary trick, as it plugs up the lady spider's genitals and stops other men impregnating it.

But that is not the only clever purpose - the male spider then has to defend his female against other spiders hoping to have a try - and without the extra weight of the sexual organs, it can fight as a much stronger warrior.

The researcher team said: 'Prior work has demonstrated that eunuch spiders are superior fighters, we here pinpoint a mechanism that enables eunuch's greater endurance.

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But if they do survive, and find themselves without one or both of their palps - their equivalent of a penis - they will protect their would-be eater, and have an advantage without the burden of their privates.

According to MSNBC, the researchers tested this by amputating either one or both palps from spiders, and exhausting them by prodding them until they stopped moving.

They found that removing one palp reduced the spider's body weight by four per cent, and removing both reduced it to nine per cent. But their endurance increased by 32 per cent and 80 per cent respectively.

The scientists speculate that the spiders fight more without their palps because they have 'nothing to live for' other than protecting potential offspring - and without the drag of their privates, they could fight for longer.